How to Clean a Dishwasher Filter Properly
Right, gear first — and let me clear something up before we start: there’s no such thing as a self-cleaning dishwasher. That sticker on the front of your Bosch or Miele saying “AquaSensor” or “Auto 3in1” is not a self-clean function — it’s a wash-water optimiser. Open the manual to page 18 of any Bosch, Miele, Westinghouse or Fisher & Paykel and you’ll find the line: “Clean filter monthly.” Most people have never opened the manual. About 80% of the dishwashers I get called to look at are not broken — they’ve got a clogged filter, the spray arms can’t get pressure, and the owner has spent six months running cleaning tablets through an empty machine wondering why their glasses still come out cloudy. Twenty minutes with a toothbrush solves it. Here’s the science of why the third filter (the one nobody knows about) matters most.
Gear you’ll need
- An old toothbrush — medium bristle, not soft
- Warm soapy water in the sink — dishwashing liquid like Morning Fresh is fine
- White vinegar — 500ml
- A microfibre cloth
- Rubber gloves
- A skewer or wooden toothpick for the spray arm holes
- A torch
- Optional: Finish Dual Action dishwasher cleaner ($8 from Woolies) for the maintenance cycle
Step 1: Pull the bottom rack out
Empty the dishwasher first. Slide the bottom rack out completely and put it on the kitchen floor — out of the way so you can kneel in front of the machine. You should now be looking down at the sump area: a circular or rectangular recess in the middle of the dishwasher floor with the lower spray arm sitting over it.
Step 2: Lift off the lower spray arm
On Bosch and Miele the lower spray arm just lifts straight up — no tools. On Westinghouse and some Fisher & Paykel models there’s a centre nut you twist anti-clockwise. Pull the arm out and look at the underside. The little jet holes are usually half-blocked with food debris, hard-water scale, or in older units, calcified gunk that looks like grey toothpaste. Run the spray arm under hot water and use the toothpick to clear every single jet hole. There are usually 12-18 holes per arm. If even three are blocked you’ve lost 25% of your wash pressure — that’s why the corner of your top rack always comes out dirty.
Step 3: Remove the coarse filter (Stage 1)
This is the big plastic mesh basket sitting in the sump. On most machines you twist it 90 degrees anti-clockwise and lift straight up. This is the filter people clean — the obvious one. Tip out the food chunks (you’ll find olive pits, prawn shells, chicken bone fragments) into the bin, not the sink, and rinse it under the hot tap. Scrub the mesh with the toothbrush. Don’t use steel wool — you’ll widen the mesh and lose filtration.
Step 4: Lift out the fine filter (Stage 2)
Underneath the coarse mesh you’ll see a flatter, finer mesh — sometimes square, sometimes round. This is where 80% of “broken dishwasher” callouts live. Lift it out gently. It’s usually coated in a beige slime that smells faintly of old fish even if you’ve never washed seafood through the machine. Soak it in hot soapy water for 5 minutes, then scrub both sides with the toothbrush. Here’s the science — the beige film is biofilm: bacteria bound together in a polysaccharide matrix that holds the colony onto the mesh. Hot water alone won’t shift it. You need the surfactant in dishwashing liquid plus mechanical scrubbing to physically break the matrix.
Step 5: Now find the micro filter (Stage 3)
This is the one nobody knows about. Look down into the sump where the fine filter just came from. There’s a flat, matte plastic disc — usually circular, sometimes with a small tab. That’s the micro filter. On Bosch you twist it anti-clockwise; on Miele you pull a small lever; on Westinghouse it just lifts out. Whatever’s stuck on this filter is the reason your glasses are cloudy and your wine glass stems have that haze. It captures particles down to 0.04mm — finer than table salt. Scrub it gently with the toothbrush; aggressive bristling can damage the woven mesh.
Step 6: Clean the sump itself
With all three filters out, use the torch to look into the bare sump. Wearing gloves, scoop out any sediment with your fingers and a paper towel. There’s often a small impeller visible — don’t force it, but do clear any food debris caught around the blades. Wipe the sump walls with a vinegar-soaked microfibre. Hard-water scale comes off with vinegar; chlorine cleaners will eat the rubber sump gasket so don’t use them. Dwell time is everything — let the vinegar sit on heavy scale spots for 3-4 minutes before wiping.
Step 7: Check the upper spray arm too
Most people forget the upper spray arm. It twists off the underside of the top rack — usually a quarter-turn anti-clockwise. The jet holes here are even smaller and they get blocked first because they fire downwards and gravity is involved. Skewer every hole, rinse from inside the arm under the hot tap so you flush any debris through the body, then twist it back on.
Step 8: Reassemble in correct order
Micro filter first (back in the sump), then fine filter on top, then coarse filter twisted to lock. Then both spray arms — bottom first, top second. If you put the coarse filter in unlocked, the next wash sprays food everywhere and you’ll be doing this all again on Wednesday. Verify the lock by gently lifting the basket — it shouldn’t move. Spin both spray arms by hand to confirm they rotate freely.
Step 9: Run a vinegar maintenance cycle
Empty machine. Put a heatproof cup with 250ml of white vinegar on the top rack, upright. Run the hottest cycle — Auto 70°C on Bosch, Sani-Rinse on Westinghouse, Intensive 75°C on Miele. The vinegar releases through the cycle and descales the heating element, the spray arms and the inside of the door from within. Don’t use vinegar more often than monthly — long-term contact will perish the rubber door seal. Once a month is the sweet spot.
Step 10: Set a monthly reminder
Same day every month. The whole job takes 15 minutes once you’ve done it twice. If your dishes start coming out gritty before the next clean is due, your filter is full — clean it early. Households that put through a lot of rice, pasta, or oats clog filters faster because those starches form a thick slurry that bonds to the mesh. I usually do this on the first Saturday of the month at the same time as the front-loader monthly clean; two appliances, one Saturday morning, sorted.
When you should NOT DIY this
If the dishwasher leaks water onto the floor during the cycle, that’s not a filter problem — it’s a door seal, a hose, or a sump pump issue, and water under a timber floor is the kind of thing you want fixed by a technician before it costs you a kitchen rebuild. Same if the machine throws an error code (E15, E24 on Bosch; F11 on Miele) — those indicate specific component failures and clearing the filter won’t help. Electrical faults (won’t power on, trips the safety switch) are a licensed-electrician job under ACCC product safety; never poke around in the wiring loom of any 240V appliance.
Common screw-ups
- Cleaning only the obvious coarse filter and missing the fine and micro filters underneath.
- Steel wool on the mesh — widens the holes and ruins filtration permanently.
- Putting the coarse filter back unlocked — sprays food everywhere on the next cycle.
- Using chlorine bleach in the sump — eats the rubber gasket and you’ll have a leak in a year.
- Vinegar cycle every wash — ruins the door seal over time, monthly maximum.
Cost & time
Materials: $3 for a toothbrush, $2 for a bottle of vinegar, a microfibre you probably already own. Total under $10 if you’re starting from nothing. Time: 15-20 minutes for the full filter pull, plus a 2-hour vinegar cycle running unattended. Compared to a $180-220 service callout in Sydney for “the dishwasher isn’t cleaning properly”, this is genuinely the cheapest fix in your home.
Before you call a technician for a dishwasher, pull all three filters and time how long it took. If you found grey slime on the micro filter, that was your problem. A service callout is $180-220 in Sydney; a toothbrush is $3 from Coles. The micro filter is the one to remember — coarse and fine you’ll figure out, but the micro hides under both and it’s where the real grime lives. Once it’s a habit, the dishwasher just works for years. And while you’re in the deep-clean kitchen mindset, the range hood filter is the other appliance most people never touch — 20 minutes in the laundry trough and it’s back to factory. Caddy out, let’s go.
